The present invention relates to an optical disk device which performs lens center servo control.
In the prior art, optical disk devices which read and record data from and to optical disks are generally widespread. Such optical disks, for example, may be Blu-Ray disks or DVDs or CDs.
As is well known in the art, the optical disk device performs tracking servo control and focus servo control during reading and recording data from and to an optical disk. The tracking servo control is the control in which the optical disk device adjusts an irradiation position of laser light to a center of tracks on the optical disk. The focus servo control is the control in which the optical disk device adjusts a focused position of the laser light upon a recording surface of the optical disk.
By performing the tracking servo control and the focus servo control, during reading and recording of the optical disk, the optical disk device not only allows the laser light to follow along a target track on the optical disk, but also ensures focusing the laser light upon the target track.
Further, the optical disk device needs to perform a high-speed and stable seek operation during reading and recording of the optical disk. By the seek operation, the optical disk device shifts a reading position or a recording position of the optical disk from the track which is currently tracking to the target track.
In the seek operation and the like, the optical disk device turns off the tracking servo control, and performs lens center servo control (hereinafter termed the “LC servo control”) by a lens error signal (hereinafter termed the “LE signal”). The LE signal shows to what extent the current position of an objective lens is away from a central position of the objective lens. The LE signal is generated by using signals output from a plurality of light receiving elements which detects reflected light from the optical disk. By the LC servo control, the optical disk device controls in such a manner that the objective lens maintains a central position corresponding to a standard voltage even if the objective lens swings due to vibration caused by rotation of the optical disk when the tracking servo control is not performed.
Japanese Laid-Open Patent Publication 2000-11404 also discloses a disk drive device which performs the above mentioned LC servo control.
However, regarding the optical disk set in the optical disk device, each optical disk has a different reflectance. In addition, regarding the characteristics of a pickup head provided in the optical disk device, each pickup head has an individual difference. Therefore, a voltage level of the LE signal generated based upon an output of the pickup head is different in each optical disk or in each pickup head.
Moreover, when an unbalanced disk is set in the optical disk device, the objective lens swings heavily due to vibration caused by rotation of the optical disk, thereby causing the objective lens to be considerably away from the above mentioned central position.
Thus, in a case where the level of the generated LE signal is too strong or too weak, the optical disk devices according to the prior art have a problem of failing to perform the proper LC servo control based upon the LE signal when the tracking servo control is turned off. Consequently, when shifting the tracking servo control from a turning off situation to a turning on situation (for example, when the above mentioned seek operation is finished), the optical disk devices according to the prior art have a problem of failing to perform the tracking servo control. Accordingly, with the optical disk devices according to the prior art, reading or recording of the unbalanced optical disk is often interrupted before its completion.
The objective of the present invention is to provide an optical disk device which can widen the capacity of a swinging amount of the objective lens due to rotation of the unbalanced optical disk, and which can dramatically reduce the interruption of the reading or recording of the optical disk before its completion.